Wire mat forming method



Jan. 17, 1967 w. D. ALLERS WIRE MAT FORMING METHOD 3 Sheets-Sheet 1Original Filed April 15, 1963 Ja1 1. 17, 1967 v w, ALLERS 3,298,403

WIRE MAT FORMING METHOD Original Filed April 15, 1963 s Sheets-Sheet 2Jan. 17, .1967 w. ALLERS 3,298,403

WIRE MAT FORMING METHOD Original Filed April 15, 1963 r 5 Sheets-Sheet 3m fix rm L U U L -.L i Z3 1 k. ZQ.; E Z9 Z9 v V K1) Q F 42 J" a UnitedStates Patent 3,298,403 WIRE MAT FORMING METHOD William D. Allers, 105W. Harris Ave., La Grange, Ill. 60525 Original application Apr. 15,1963, Ser. No. 273,227. Di-

vided and this application Nov. 24, 1965, Ser. No.

6 Claims. Cl. 140-921 This application is a division of my copendingapplication Serial No. 273,227, filed April 15, 1963, now abandoned.

j The invention of thisaapplication relates to a method of forming awire mat particularly suitable for use in prestressing concrete sheetsand other members.

In Patent No. 3,084,910, issued April 9, 1963, a method and apparatusare disclosed for forming prestressed concrete sheets. An arrangement oftensors is provided for tensi-oning a plurality of wires over a bed,each tensor in its preferred form comprising a horizontal rod carried bya plurality of arms or shoes which pivot at their ends about ahorizontal pivot line parallel with but spaced from the axis of the rod.A power-operated lever is connected to the tensor for slowly pivoting itto shift the horizontal rod downwardly and outwardly away from the bed,thereby stretching andtensioning the wires which are looped about therod and which span the bed. When the self-locking tensor is fullylowered and the wires have reached maximum predetermined tension, alayer of wet concrete is applied to the bed and, after the concrete hasfully hardened, the tensor is disconnected from the exposed ends of theimbedded wires.

For effective stressing of the concrete sheet or other member, it isessential that the stretched and highlytensioned wires be securelyanchored within the concrete. Otherwise, the wires would contract assoon as they are cut or disconnected from the tensor and the concrete inwhich such wires are imbedded would not be stressed. It is for thisreason, among others, that multiple strand twisted wire is preferred;the uneven contour of such wire plays an important part in achieving asecure interlock between that wire and the surrounding concrete.

Despite its important advantages, twisted wire has significantdisadvantages which makes it difiicult, expensive, and even dangerous touse in forming prestressed concrete members. A particular problemconcerns the wide range and dangerously unpredictable level of maximumtension which such wire is capable of withstanding depending uponwhether it is tensioned along a straight or curved line. Where'the wirecurves sharply, as where it is looped around the horizontal rod of atensor, the different radii of curvatures for the various strands at anygiven point of contact with the tensor rod results in unequal stressingof the strands. The outermost strand at any given point is under greaterstress and tends to cut into the strand or strands in contact with thesurface of the tensor rod. Should one strand be se'vered by an adjacentstrand, a type of chain reaction occurs with many strands breaking,often at the same point, and the wire, with its tension suddenlyrelieved, lashing or whipping about. It should be noted that if anyslippage or relative movement occurs between the wire and the smoothsurface of the tensor rod during the tensioning step, such relativemovement significantly increases the possibility of the self-severingaction of the twisted wire.

Another problem relates to the difficulty of determining the stresslimits of twisted wire because of the slight st-retchability whichinherently results from its twisted character. Even where such wire iscut into precisely equal lengths and each length is provided with itsown terminals on opposite sides of the bed, the variations in the stresslimits of each stretch of wire over the bed may give rise to breakageproblems. Where a single piece of twisted wire is strung back and forthover the bed to form an integral wire mat, the danger of breakage issubstantially greater because of the tendency of the various stretchesto equalize their tensions, and thereby slip over the smooth roundedsurface of the tensor rod, as the tensor is shifted downwardly into itswiretensioning position.

Accordingly, it is a principal object of the present invention toovercome the aforementioned defects and disadvantages in the methods offorming prestressed concrete members. Another object is to provide amethod of forming a wire mat for use in forming prestressed concretemembers, such mat having all of the important advantages of twisted wirewithout the above-described disadvantages thereof. A further object istoprovide a method of forming a mat of twisted wire which may be used inconjunction with the prestressing apparatus and method disclosed in theaforementioned patent without danger that one strand will tend to severanother against the outer surface of the tensor rod.

A further specific object is to provide a method of forming a mat havingstretches of wire of substantially identical length and stresscharacteristics. It is a further object to provide a method which issuitable for forming a single strand of wire into a mat having twistedwire stretches of any desired length.

Other objects will appear from the specification and drawings in which:

FIGURE 1 is a broken top plan view of a bed and wire tensioningapparatus, the apparatus holding in fully tensioned state a wire mat;

FIGURE 2 is a side elevational view of the bed, ap-

paratus and mat shown in FIGURE 1;

FIGURE 3 is an enlarged broken perspective view illustrating in detailthe relationship between the tensor of the apparatus and the wire mat;

FIGURE 4 is a broken perspective view illustrating the structuraldetails of the mat;

' FIGURE 5 is a perspective view of an apparatus for use in forming themat shown in FIGURE 4;

FIGURE 6 is an enlarged broken top plan view illustrating anintermediate step in the formation of the mat;

FIGURE 7 is a top plan view similar to FIGURE 6 but of reduced scale andillustratin a subsequent twisting step in the formation of the mat;

FIGURE 8 is a broken and somewhat diagrammatic plan view of a wire matprior to the twisting of adjacent stretches thereof;

FIGURE 9 illustrates one way in which the wire shown in FIGURE 8 may betwisted to form a completed mat;

FIGURE 10 illustrates a second way in which the wire of FIGURE 8 may betwisted to form a completed mat;

FIGURE 11 illustrates a third way in which the wire of FIGURE 8 may betwisted to form a completed mat.

Referring to FIGURES 1-11 of the drawings, the numeral 10 generallydesignates a mat which is formed from a single piece of wire or otherfilament. The word wire is here used to mean a filament formed of metalor any other material having the requisite characteristics of strengthand durability. While in most instances the wire is preferably formed ofsteel or other suitable metal, it is to be understood that the wire mayalternatively be formed of nylon or other plastics.

In FIGURES 1, 2 and 3 the mat is shown in use in conjunction With a bedA and tensor B of the type generally disclosed in Patent No. 3,084,910to which reference has previously been made. The bed consistsessentially of a slab 11 having a top surface 12 in the shape of aconcrete member 13 to be formed thereon. In the illustration given,surface 12 is flat and member 13 constitutes a thin concrete sheet. Onopposite sides of the bed are upstanding posts 14 and 15. Posts 14 bearagainst one side of slab 11 and brace the foundation 16 as well as thehorizontal rod 17 which is held tightly against the posts by the highlytensioned wires looped thereabout.

The series of spaced upstanding posts along the opposite side of theslab areinterposed between that slab and an inclined platform 18. Theplatform is horizontally elongated and slants transversely upwardlytowards the series of posts 15 to provide an inclined supporting surfacefor tensor B.

The tensor consists essentially of a horizontal rod 19 which isrotatably supported in the end notches 20 of a plurality of inwardlyextending pivot arms or shoes 21. Allof the spaced parallel arms arerigidly interconnected by a connecting bar 22 and the inner ends of thearms are rounded (in vertical planes) and bear against posts 15 andplatform 18. Thus, the tensor B is capable of pivoting about a pivotline parallel with and spaced inwardly with respect to the axis oftensor rod 19, the range of pivotal movement being represented in FIG-URES 2 and 3 by the raised position of FIGURE 3 (also shown in brokenlines in FIGURE 2) and the lowered position of FIGURE 2.

' When the tensor is in its fully lowered position, the axis of rod 19is spaced below the pivot line of the tensor and the tension of thestretched wire mat effectively locks the tensor in place. During thewire-tensioning operation, as the tensor is pivoted downwardly, rod 19is free to rotate about its own axis and within the notches 20* of thepivot arms, thereby eliminating or reducing slipping contact between thewire and the rod. Downward pivoting movement of the tensor is mosteasily accomplished by connecting a suitable lever extension (not shown)to the tensor to increase the mechanical advantage of the applied force.Such a lever assembly and a form of winch used in connection with itsoperation are fully disclosed in the aforesaid copending applicationand, since they form no part of the present invention, need not bedescribed in detail herein.

Mat 10 consists of a single strand of wire which extends between thestationary horizontal -rod 17 and tensor rod 19. With the exception ofthe terminal stretches, all of the stretches of wire which extend backand forth between the stationary rod and the tensor rod are ofsubstantially identical length. Since the rod 17 extends along the samehorizontal plane as the uppermost edge portion of platform 18, thestretches of fully tensioned wire extend in the same horizontal planebetween spaced points along a pair of spaced parallel lines.

Referring to FIGURES 4, 9 and 1, it will be observed that adjacentstretches of the wire have their intermediate portions twisted togetherto provide a plurality of paral lel double-strand intermediate sections23. At one end of each intermediate section is a single-strand loop 24which, in the illustrations given, is fitted over stationary rod 17. Atthe opposite ends of the intermediate sections (and along the oppositeside of the mat) are a plurality of single-strand loops 25 whichinterconnect adjacent intermediate sections of the mat. In contrast tobridging loops 25, each of the loops 24 is closed and extends to only asingle intermediate section.

The terminal stretch of wire 26 returns to the terminal intermediatesection 27 so that such section differs from the other intermediatesections 23 in being formed of three strands twisted together. As aresult of such construction, closed loops 24 and 28 are provided atopposite ends of each terminal intermediate section 27. The extreme endof terminal stretch 26 may be aflixed to the remaining strands of theintermediate portion 27 by any suitable connecting means; however, ithas been found that if the mat is of sufficient size and the terminalintermediate portion 27 is sufficiently twisted, no additionalconnection between the three strands of the section 27 is required.

Each of the two-strand intermediate sections 23 has an identical numberof twists. The terminal intermediate portions 27 may have one or morefewer twists to comensate for their greater thickness. The result is amat having a plurality of integral elements (each element consisting ofend and intermediate sections) of substantially identical overall ortotal length.

The mat 10 is formed from a single strand of wire by the methodillustrated in FIGURES 5 through 7. The single-strand wire iscommercially available on large spools and, as a preliminary step in theformation of the mat, the wire 29 is unwound from the spool (not shown)onto reel 30. The reel may be generally H-shaped composed of a pluralityof interconnected side, end, and intermediate members 31, 32, 33,respectively. The reel is rotatably mounted upon a horizontal shaft 34which passes through the centers of intermediate members 33, therebyfacilitating the winding of the Wire 29 under generally uniform tensionupon the reel. End members 32 are all parallel with each other and arepreferably provided with a series of spaced-apart arcuate recesses 35,each of the recesses being adapted for slidably supporting only a singlecoil of the wire 29 wrapped about the reel. The wire is wound about thespool with a degree of resistance suflicient to place equal lengths ofwire about each turn of the reel.

After the wire is fully wound upon the reel but has not been severedfrom the supply spool, two series of pulleys 36 and 37 are brought intocontact with the inner surfaces of the coils of wire as shown in FIGURE5. The two sets of pulleys 36 and 37 are rotatable about axes which areparallel with each other and with the end members 32 of the reel. Eachpulley is independently rotatable about its own axis, and at least oneof the sets is constructed so that the pulleys thereof may also berotated about the axes of their mountings. In the illustration given,the pulleys of set 36 are independently rotatable about the axles 39 ofindividual mounting elements 40, although it is to be understood (forreasons which will appear hereinafter) that the pulleys of set 37 may besimilarly mounted, rather than being mounted upon a single shaft 38. Itwill also be noted that the spacing between the pulleys of each setcorresponds with the spacing between the recesses 35 of each end member32. Therefore, as the two sets of pulleys are drawn outwardly inopposite directions, the groove of each pulley receives a portion of asingle coil of the wire 29 wound about the reel 30.

The particular carriage means used to support each set of pulleys foroutward movement with respect to the reel may vary considerablydepending upon the size, location and capacity of the particularinstallation. Whatever the design of the particular carriage means, itis essential in forming a rectangular mat that the axes of the two setsof pulleys remain at all times in parallel relation with each other.Since the wire 29 remains connected to the supply spool (not shown), andsince the wire is 3 freely slidable Within the recesses 35 of endmembers 32, outward movement of the two sets of rollers produceslongitudinal sliding movement of the wire 29 about the reel. Additionalwire, as it is required, is provided by the supply spool. Outwardmovement of the pulleys is continued until the stretches of wireextending back and forth between the parallel rolls of pulleys are of apreselected length. The wire is severed from the supply spool and, withopposite ends of the wire entrained about the pulleys anchored securelyin place, a predetermined outward force is applied to the two sets ofpulleys 36 and 37 to produce uniform tension in all of the stretches 29of w1re.

Where only a relatively small mat is desired, the wire may be wound uponthe reel in uniformly tensioned condition, and thereafter removed fromthe reel, by disassembling, partially collapsing, or otherwise reducingthe size of the reel, for placement of the wire upon an arrangement ofopposing pulleys.

Thereafter, each of the pulleys 36 is rotated about a radial axisgenerally parallel with the stretches of wire extending therefrom(FIGURE 7). The pulleys 36, with the possible exception of terminalpulleys 36a, are rotated an identical number of turns in the same ordifferent direction. The terminal pulleys 36a may be rotated one or morefewer turns in the same or different direction because of the fact thatthe terminal intermediate sections 27 comprise three strands of wirerather than only two strands as in intermediate sections 23. When thewire is fully twisted, the looped end sections 24, 25 and 28 are removedfrom the pulleys. The result is a mat formed of wire having generallyparallel elements of equal length, each element consisting of a doublestrand intermediate section (except for the terminal elements) andsingle strand end sections.

Since the end sections are only of single strand construction, they maybe looped about the horizontal movable tensor rod 19, or the stationaryvertical tensor rods 17, of the apparatus illustrated in FIGURE 1, andthe wire elements of the mat may then be stressed or stretched withoutdanger that one strand might sever another strand in contact with thetensor rods. Furthermore, since the elements of the mat are of identicallength, with all of the two-strand intermediate portions having anidentical number of turns or twists, there is no appreciablelongitudinal sliding movement of the wire over the tensor rods during atensioning operation. These important results are achieved while at thesame time providing a mat having wire elements with twisted intermediatesections. Such sections constitute the principal length of each wireelement and are essentially the only sections imbedded in the concretemember formed thereabout. Therefore, because of the twisted character ofthe imbedded wire, the chances of wire slippage in the finished concreteproduct are substantially eliminated.

FIGURES 8 through 11 illustrate different Ways in which the same wire,previously stretched and preformed by the means illustrated in FIGURESand 6, may be twisted to form mats of different configuration. Startingwith the wire with parallel stretches 29 as illustrated in FIGURE 8, thelooped ends designated by the letters A, B and C may be rotated bypulleys 36 in the manner already described to form the completed mat(FIG- URE 9) in which A, B and C become closed loops 24. Loops D-G,supported by pulleys 37 all carried upon the same shaft 38, form openloops 25 and closed loop 28 in the final mat 10.

The same wire of FIGURE 8 may be twisted differently to form themodified mat 10 illustrated in FIGURE 10. Mat 10' is formed bysuperimposing loops D and E, and twisting them simultaneously whileholding loops A, B and C stationary. Loops F and G are separatelytwisted in the same manner as composite loops D, B. As in mat 10, theintermediate portions 23' of mat 10 are twisted the same number ofturns, whereas the terminal intermediate portion 27' has a lesser numberof turns to form twisted elements of equal length. One advantage of mat10' over mat 10 lies in a more secure connection between the terminalstretch 26' and the remaining wire portions which form the terminalelement.

The mat 10" of FIGURE 11 is similar to the mat 10' of FIGURE 10 exceptthat the pulleys supporting loops A, B and C have been rotated as wellas the pulleys supporting loops D-E, F and G. In other wonds, mat 10 isformed by twisting the wire of FIGURE 8 from all of the looped ends, theapparatus for performing such an operation consisting, as alreadyindicated, of opposing sets of independently mounted pulleys 36.

From the foregoing, it is believed apparent that mats having singlestrand looped end portions and twisted intermediate elements may assumea variety of configurations. All of the elements of such mats are ofsubstantially identical length and, therefore, there is no appreciablelongitudinal sliding movement of the wire over the tensor rods during atensioning operation. Since the portion of the mat imbedded in theconcrete consists primarily of twisted wire, the mat is firmly anchoredin place and is well able to perform its essential function inprestressing the surrounding concrete body.

While several embodiments have been disclosed in considerable detail forpurposes of illustration, it will be understood by those skilled in theart that many of these details may be varied without departing from thespirit and scope of the invention.

I claim:

1. In a method of forming a mat for use in prestressing concretemembers, the steps of extending a single strand of wire back and forthbetween spaced opposing series of pulleys, each pulley of one of saidseries being associated with an individual mounting, each of saidmountings being independently rotatable, urging said series of pulleysapart while simultaneously holding the ends of said wire againstlongitudinal movement to tension uniformly the stretches of wire betweensaid pulleys, and thereafter rotating said mountings to twist adjacentpairs of said stretches of wire together to form a mat of interconnectedwire elements having twisted intermediate sections and untwistedsingle-strand end loops.

2. The method of claim 1 in which said pulleys are arranged in twospaced parallel series, said adjacent pairs of said stretches of wirebeing twisted equally to provide a mat having wire elements withintermediate sections of equal numbers of turns.

3. In a method of forming a mat for use in prestressing concretemembers, the steps of extending a single strand of wire back and forthbetween two spaced opposing series of pulleys, each pulley of one ofsaid series being associated with an individual mounting, each of saidmountings being independently rotatable, separating said series ofpulleys while at the same time permitting longitudinal movement of saidwire to extend the length of the stretches of wire between said pulleys,urging said series of pulleys apart while simultaneously holding theends of said wire against longitudinal movement to tension uniformlysaid stretches of wire, and thereafter rotating said mountings to twistadjacent pairs of said stretches together to form a mat havinginterconnected wire elements with twisted intermediate sections anduntwisted single-strand end loops.

4. The method of claim 3 in which said series of pulleys extend withtheir axes along spaced parallel lines, said adjacent pairs of saidstretches of wire being twisted equal numbers of turns to form aplurality of substantially identical interconnected wire elements.

5. In a method of forming a mat for use in prestressing concretemembers, the steps of winding a single strand of wire about a reel toform a plurality of substantially identical coils of wire, expandingeach coil by urging opposite portions thereof outwardly in oppositedirections 7' 8 while at the same time permitting longitudinal movementReferences Cited by the Examiner of the wire thereofluniformlytensioning said coils by UNITED STATES PATENTS urging said oppositeportions outwardly in opposite directions while preventing longitudinalmovement of the 3 'ggx 1351; end portions of said wire, and thereaftertwisting each 5 coil of wire to form a plurality of elongated and inter-FOREIGN PATENTS connected wire elements having twisted intermediate sec-319 555 3/1920 Germany, tions and untwisted single-strand end loops.661,155 11/1951 Great Britain.

6 The method of claim 5 in which all of said coils I other than theterminal coils are twisted an identical ml CHARLES LANHAM Pnmary Examme"number of turns. L. A. LARSON, Assistant Examiner.

1. IN A METHOD OF FORMING A MAT FOR USE IN PRESTRESSING CONCRETEMEMBERS, THE STEPS OF EXTENDING A SIGLE STRAND OF WIRE BACK AND FORTHBETWEEN SPACED OPPOSING SERIES OF PULLEYS, EACH PULLEY OF ONE OF SAIDSERIES BEING ASSOCIATED WITH AN INDIVIDUAL MOUNTING, EACH OF SAIDMOUNTINGS BEING INDEPENDENTLY ROTATABLE, URGING SAID SERIES OF PULLEYSAPART WHILE SIMULTANEOUSLY HOLDING THE ENDS OF SAID WIRE AGAINSTLONGITUDINAL MOVEMENT TO TENSION UNIFORMLY THE STRETCHES OF WIRE BETWEENSAID PULLEYS, AND THEREAFTER ROTATING SAID MOUNTINGS TO TWIST ADJACENTPAIRS OF SAID STRETCHES OF WIRE TOGETHER TO FORM A MAT OF INTERCONNECTEDWIRE ELEMENTS HAVING TWISTED INTERMEDIATE SECTIONS AND UNTWISTEDSINGLE-STRAND END LOOPS.